Argyll Robertson Pupil (ARP)

Definition and Clinical Features

The Argyll Robertson pupil (ARP) is a highly specific pupillary abnormality characterized by a pupil that is small (miosis) and irregular in shape. Its hallmark feature is the failure to constrict in response to light (reflex iridoplegia), while still retaining the ability to constrict sharply during accommodation (when the eyes converge to focus on a near object). This phenomenon is classically referred to as light-near pupillary dissociation. A useful clinical mnemonic to remember this is ARP: Accommodation Reflex Present.

Clinical Examination Technique

Testing for the Argyll Robertson pupil requires careful evaluation of both the light reflex and the near response. Because the direct and consensual light reflexes are lost, testing the accommodation reaction can actually be performed with the pupil directly illuminated. This technique can make it much easier to observe the constrictive response to accommodation, which is otherwise notoriously difficult to see when the pupil is already very small or in individuals with dark irides.

Additional clinical features include an incomplete or poor response to standard mydriatic (dilating) drops. Although involvement is typically bilateral, it is frequently asymmetric, leading to noticeable anisocoria (unequal pupil sizes).

Causes and Associated Conditions

The Argyll Robertson pupil was originally described by Douglas Argyll Robertson in 1869 in the context of late-stage neurosyphilis, specifically tabes dorsalis. If neurosyphilis is suspected, a helpful associated clinical finding is the loss of deep pain sensation, which can be assessed by vigorously squeezing the Achilles tendon (known as Abadie’s sign).

However, there are a number of other recognized causes of ARP besides neurosyphilis, including:

• Multiple sclerosis
• Viral encephalitis
• Diabetes mellitus (severe diabetic autonomic neuropathy)
• Syringobulbia
• Sarcoidosis
• Lyme disease
• Pinealoma (and other dorsal midbrain tumors)
• Herpes zoster
• Hereditary motor and sensory neuropathies (e.g., Charcot-Marie-Tooth disease; Dejerine-Sottas hypertrophic neuropathy)

It is important to note that miosis and pupil irregularity are inconstant findings in some of these non-syphilitic situations. When light-near dissociation occurs without the classic small, irregular pupil, the term pseudo-Argyll Robertson pupil is preferred.

Pathophysiology and Neuroanatomy

The precise neuroanatomical substrate of the Argyll Robertson pupil remains a subject of debate. The most widely accepted theory posits a highly localized lesion in the tectum of the rostral midbrain, proximal to the oculomotor (Edinger-Westphal) nuclei. This specific location would interrupt the dorsal light reflex pathway (crossing in the posterior commissure) while sparing the more ventrally located pathways mediating the near/accommodation response.

In conditions like multiple sclerosis and sarcoidosis, magnetic resonance imaging (MRI) has demonstrated lesions in the periaqueductal gray matter at the level of the Edinger-Westphal nucleus. However, because these cases often lack the classic miosis, they may be better classified as pseudo-Argyll Robertson pupils. Alternatively, some authorities suggest that the classic ARP might result from a partial oculomotor (III) nerve palsy or a highly specific, spirochete-induced lesion of the ciliary ganglion.

 

References

Argyll Robertson D. Four cases of spinal myosis [sic]: with remarks on the action of light on the pupil. Edinburgh Medical Journal 1869; 15: 487-493

Dacso CC, Bortz DL. Significance of the Argyll Robertson pupil in clinical medicine. American Journal of Medicine 1989; 86: 199-202

 

Cross References

Abadie’s sign; Anisocoria; Light-near pupillary dissociation; Miosis; Pseudo-Argyll Robertson pupil